For example, when a workpiece, such as a steel plate is cut, a gas cutting method has been widely used in which a cutting start point in the workpiece is heated to a temperature at where an oxidation reaction can be carried out by a preheating flame generated at a preheating hole, and the workpiece is burned and melted to be cut by injecting oxygen gas with a high purity from a cutting oxygen gas hole toward the heated portion.
In the gas cutting method, while the cutting start point in the workpiece is heated and while the workpiece is cut, a hydrocarbon-based gas and an oxygen gas are supplied as fuel gas to generate a preheating flame. However, a hydrogen gas has recently been used instead of the hydrocarbon-based gas (For example, Patent Document No. 1).
According to this gas cutting method, it is necessary to supply a large amount of a hydrogen gas to the preheating hole even when a workpiece is heated. That is, this gas cutting method has a drawback of cost.
Therefore, a technical solution, which can heat the workpiece sufficiently when the workpiece is heated with the preheating flame, and solves the drawback of cost, is desired.